This invention relates to an anchor used to fasten an object to a wall or ceiling of a type not accessible to the back, by means of a screw.
It is usually impossible to fasten an object to a brittle wall such as a plasterboard simply by driving a nail or screw into the wall because the nail or screw loosens. To prevent loosening of the nail or screw, it is necessary to stick a patch of reinforcing metal on the back of the wall before the wall is erected so that the nail or screw pierced through the wall is driven into the metal patch. Once the wall is erected, it is impossible to change the position of the metal patch if there is only a little space behind the wall. Thus, a nail or screw can be used at the predetermined position only.
In other conventional arrangements, as disclosed in Japanese patent publications 36-18855 and 52-154474, instead of sticking a metal patch on the back of a wall before the wall is erected, a hole is drilled in a wall that has already been erected, and an anchor is inserted into the space behind the wall. With the anchor located behind the wall, a bolt is driven through the wall and threaded into the anchor to securely fasten an object to the wall.
The anchor of the publication 36-18855 comprises a backing plate formed with a threaded hole, a tape attached to the plate, and a ring slidably mounted on the tape. In use, the plate is inserted through a starting hole formed in a wall into the space behind the wall, and the ring is slid along the tape and fitted in the starting hole. The tape is then pulled until the plate is pressed against the back of the wall. Then an operator drives a screw into the threaded hole of the plate by turning it with one hand while pulling the tape with the other hand to keep the plate pressed against the back of the wall. This work is troublesome and difficult.
When the screw has been threaded sufficiently into the threaded hole, the portion of the tape protruding from the surface of the wall is cut, and then the screw is tightened further to securely fasten an object to the wall.
The anchor of the publication 52-154474 comprises a backing plate formed with a threaded hole, a pair of resilient legs secured to the bottom of the plate to extend perpendicular to the plate, and a slide ring slidably mounted on the legs. In use, the plate is inserted through a starting hole formed in a wall into the space behind the wall by bending the legs so as to be parallel to the plate, and the ring is slid along the legs and fitted in the starting hole. The portions of the legs protruding from the surface of the wall are then cut, and a screw is threaded into the threaded hole of the backing plate with an object pressed against the surface of the wall. Since the position of the slide ring is determined by serrations formed on the legs, it can be positioned only stepwise, so that the ring cannot be securely fitted in the starting hole. This tends to cause the ring and thus the plate to turn when the screw is driven in.
In either of the above conventional arrangements, no means are provided for preventing the backing plate from turning. Thus, the backing plate tends to turn when the screw is threaded into its threaded hole.
In any of the above conventional arrangements, if there remains, even slightly, a portion of the tape or legs protruding from the surface of wall, this portion will be sandwiched between the wall surface and the object fastened when the screw is tightened, creating a clearance between the wall and the object to be fastened. Such a clearance will cause the backing plate to turn when the screw is driven in.
An object of the invention is to provide an anchor having a means for preventing its backing member located behind a wall to which an object is to be fastened from turning or getting off position when a screw is threaded into a hole formed in the backing member.